Mini-gastrin analogue, in particular for use in cck2 receptor positive tumour diagnosis and/or treatment

ABSTRACT

A gastrin analogue shows high uptake in CCK-2 receptor positive tumors and simultaneously a very low accumulation in the kidneys. This is achieved by a mini-gastrin analogue PP-F11 having the formula: PP-F11-X-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Y-Asp-Phe-NH 2 , wherein Y is an amino acid replacing methionine and X is a chemical group attached to the peptide for diagnostic and/or therapeutic intervention at CCK-2 receptor relevant diseases. Very suitable compounds with respect to a high tumor to kidney ratio are mini-gastrin analogues with six D-glutamic acids or six glutamines. These compounds still possess a methionine which can be oxidized easily which is a disadvantage for clinical application under GMP due to the forms which may occur. The elimination of the methionine leads to a lower affinity to oxidation which in general favors the tumor-kidney-ratio. Ideally, the methionine is replaced by norleucine. This PP-F11N mini gastrin exhibits currently the best tumor-kidney-ratio and is the most promising candidate.

The present invention relates to a mini-gastrin analogue and to its use in CCK2 receptor positive tumour diagnosis and/or treatment.

G protein-coupled receptors (GPCR) are used as target proteins for radiolabelled peptides since the early 90's. The somatostatin receptor was the prototype for radionuclide imaging and therapy with peptides (Lit) resulting in a clinical first line therapies for neuroendocrine tumors with Y-90 and Lu-177 labelled derivatives of octreotide (Lit). Several radiolabelled peptides were tested for the possibility to target overexpressed GPCR on tumours including gastrin realising peptide analogues (GRP), glucagon-like peptide 1 analogues (GLP-1), neurotensin analogues (NT) or neuropeptide Y analogues (NPY) (Macke, Reubi J Nucl Med 2008; 49:1735-1738). An additional very interesting target is the cholecystokinin-2 receptor (CCK-2 R). This receptor is mainly expressed on medullary thyroid carcinomas (MTC), small cell lung cancers (SCLC) and stromal ovarial tumors (Reubi, Int J Cancer. 1996 and Reubi, Cancer Res. 1997). Radiolabelled gastrin analogues are good candidates for targeting imaging and therapy. It was shown that In-111 labelled gastrin analogues are superior for detecting MTC compared to OctreoScan-111 and give additional information on neuroendocrine tumours particularly if they are negative in somatostatin receptor scintigraphy (Endocr Relat Cancer. 2006 December; 13(4):1203-11.; Eur J Nucl Med Mol Imaging. 2006 November; 33(11):1273-9).

But due to the high kidney uptake the radiolabelled peptides could not be used for therapy. The high kidney uptake is correlated with the six negatively charged glutamic acids. 12 gastrin related compounds were designed, synthesised and compared as 111In labelled compounds. The best compounds with respect to a high tumour to kidney ratio are the mini-gastrins with six D-glutamic acids or six glutamines. These compounds still possess a methionine which can be oxidised easily. This is a disadvantage for clinical application because the receptor affinity is dramatically decreased after oxidation of the methionine and the production under GMP may be hampered dramatically.

A high potential for a significant improvement of the therapy and the image generation with patients having metastasized medullary thyroid carcinomas (MTC), small cell lung cancers (SCLC) and further CCK-2 receptor positive tumours has a specific labelling of the tumour cells with radio-labelled gastrin analogue. Basis for this finding is the proof of an over-expression of the respective CCK-2 target receptor at 92% of the investigated MTC, said proof being yielded by in-vitro studies [Reubi 1997]. Furthermore, the same working group identified the same over-expression of the CCK-2 target receptor at 57% of small cell lung cancers, 65% of astrocytomes and 100% of stromal ovarial tumours.

First therapy studies (phase 0 study) had been executed at eight patients having advanced metastasized medullary thyroid carcinomas. For two patients a partial remission was achieved, four patients showed a stabilization of the formerly strong progressive course of the cancer disease MTC after a therapy with ⁹⁰Y-labelled mini-gastrin analogue. This study had to be stopped due to the nephrotoxicity of the therapy in terms of a strong accumulation of the substances used in said assay in the kidneys.

With support of the European COST initiative (European Cooperation in Science and Technology), in the meantime a plurality of significantly improved radio-labelled gastrin-analoga have been synthesized by various working groups and have been investigated for their characteristics. As compared to the old gastrin analogue, these younger substances possess a significantly higher tumour-to-kidney ratio with respect to the absorption in human tissue [Laverman 2011, Polenc-Peitl 2011, Ocak 2011, Fani 2012]. Currently, out of these younger gastrin analogues, ¹⁷⁷Lu-PP-F11 (the linear mini-gastrin analogue with six D-Glu residues, hereinafter called PP-F11) exhibited best properties for future radio nuclide therapy due to its high favorable accumulation in the tumor accompanied by a low accumulation in the kidneys.

It is therefore the objective of the present invention to provide gastrin analogue which show even better accumulation in CCK-2 receptor positive tumours by simultaneously very low accumulation in the kidneys.

This objective is achieved according to the present invention by a mini-gastrin analogue PP-F11 having the formula: PP-F11-X-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Y-Asp-Phe-NH₂, wherein Y stands for an amino acid replacing methionine and X stands for a chemical group attached to the peptide for the purpose of diagnostic and/or therapeutic intervention at CCK-2 receptor relevant diseases.

In particular, very suitable compounds with respect to a high tumour to kidney ratio are mini-gastrin analogues with six D-glutamic acids or six glutamines. These compounds still possess a methionine which can be oxidised easily which is a disadvantage for clinical application under GMP due to the forms which may occur. Therefore, the replacement of the methionine by a non oxidizable isosteric amino acids but retaining the biological activity leads to a compound with no oxidation potential. This avoids the oxidation during storage and production which could be lead to lower affinity compound resulting in a low tumor to kidney ratio.

In a preferred embodiment of the present invention, the methionine is replaced by norleucine. This so-called PP-F11N mini gastrin exhibits currently the best tumour-kidney-ratio and is therefore the most promising candidate for clinical applications. With respect to radio cancer treatments, X may stand for a radio nuclide including the attachment group like a chelator for radiometals such as ¹⁷⁷Lu or ⁹⁰Y or ¹¹¹In, or a prostethic group for non mtelas like F-18 or radioiodines. In order to improve the medical imaging, the X may for an optically active chemical compound, such Alexa Fluor® 647, IRDye 680RD or DY-700 and for optical therapeutic application it may be a photosensitizer like Photofrin, Forscam or Photochlor. For both application the active chemical compound may be a optical active nanopartical In order to support the chemotherapeutic intervention, X may stand for a chemotherapeutic active compound, such as gemcitabine, doxorubicine or cyclophosphamide. The delivery of the described agents may be done by a nanoparticle or liposome as X whereas they are loaded with chemotherapeutic agents.

With respect to the use of the inventive mini gastrin, a diagnostic intervention at CCK-2 receptor relevant diseases and/or a therapeutic intervention at CCK-2 receptor relevant diseases is foreseen.

Preferred embodiments of the present invention are hereinafter described in more detail with respect to the attached drawings which depict in:

FIG. 1 the structural design of PP-F11N starting from a mini-gastrin analogue PP-F11 being arised from the COST initiative;

FIG. 2 the biodistribution of PP-F11, PP-F11N and PP-F11 ox (oxydized PP-F11) after four hours in the CD1 nu/nu mice model;

FIG. 3 the bio diversion of PP-F10, PP-F10N and PP-F10 ox (oxydized PP-F10) after four hours in the CD1 nu/nu mice model; and

FIG. 4 the stability of diverse mini-gastrin analogues with the course of the time.

FIG. 1 illustrates the mini-gastrin analogue PP-F11 that has been derived from the COST initiative mentioned above. The modified mini-gastrin analogue PP-F11N has been achieved by the exchange of the oxidizable amino acid methionine with norleucin. DOTA stands for 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid which is an organic compound with the formula (CH₂CH₂NCH₂CO₂H)₄. The molecule consists of a central 12-membered tetraaza (i.e., containing four nitrogen atoms) ring. DOTA is used as a complexing agent, especially for lanthanide ions. Its complexes have medical applications as contrast agents and cancer treatments.

PP-F11N has been investigated according to the CD1 nu/nu mice model. As compared to PP-F11, the mini-gastrin analogue PP-F11N exhibited a significant higher tumor uptake which also leads to a very favorable tumor-noise ratio with very few accumulation in the kidneys. FIG. 2 illustrates the biodistribution of PP-F11, PP-F11N and oxidized PP-F11 ox (oxidized PP-F11) after 4 hours in the athymic CD1 nu/nu mice model. Tumour positive: with human CCK-2 receptor transfected A431 cells on one side of the mouse; tumor negative: CCK-2 receptor negative A431 cells on the other side of the mouse. The effect of the higher tumor uptake by the exchange of methionine with norleucine is specifically apparent with compounds having the DGlu6 sequence, different from compounds having a sequence with DGLn6 which is referred to as PP-F10.

FIG. 3 shows the results for PP-F10 and PP-F10N and PP-F10 ox (oxidized PP-F10) in comparison to the results shown in FIG. 2. The structural formula of the PP-F10's is given below:

PP-F10: DOTA-DGln-DGln-DGln-DGln-DGln-DGln-Ala-Tyr- Gly-Trp-Met-Asp-Phe-NH₂ PP-F10N: DOTA-DGln-DGln-DGln-DGln-DGln-DGln-Ala-Tyr- Gly-Trp-Nle-Asp-Phe-NH₂; PP-F10 ox: DOTA-DGln-DGln-DGln-DGln-DGln-DGln-Ala-Tyr- Gly-Trp-Met(ox)-Asp-Phe-NH₂.

A promising tumor uptake can therefore not be seen in FIG. 3 since other organs, such as the pancreas, the kidney and the bones take partially even higher doses than the targeted tumor.

FIG. 4 illustrates the pharmacologic stability of PP-F11N as compared to PP-F11, PP-F10N and PP-F10 (all radio-labelled with ¹⁷⁷Lu. The stability has been checked in human serum; the measurements of the metabolites have been executed by means of HPLC. The mini-gastrin analogue PP-F11N according to the present invention shows the highest pharmacologic stability of all probands.

Materials: The peptides (PP-F10, PP-F10N, PP-F11 and PP-11N) were synthesized by PLS (Heidelberg, Germany) by the Merrifield method. All the chemicals were purchased from Sigma-Aldrich (Buchs, Switzerland). A431 cells (cell line squamous cell carcinoma) were stably transfected with cDNA encoding for CCK2R or with empty vector (‘mock-transfected’)¹ and were a kind gift from L. Aloj (Naples). Lu-177 was purchased from ITG (Germany, Munich). The peptide conjugates were complexed with natural ^(nat)Lu.

The labeling of the mini-gastrins has been executed under the following circumstances:

System for HPLC Analysis:

System: Pump Varian Prostar 2030.01, Diode Array 330.71, Autosampler 410, Packard Radiomatic Flow-One\

Column: Stability 120 BS-C23 3 μm 150*4.6 mm, Dr. Maisch

Gradient:

% H2O + 0.1% % ACN + 0.1% Min TFA TFA 0 90 10 3 90 10 15 5 95

System for the Purification:

Pump 1: Waters 515, Pump 2: Hitachi L-7000, Knauer UV Detector K2510, Radio-Monitor Eberline, interface SS420X, EZstart

Rheodyne manual injector

Column 1: Stability 120 BS-C23 3 μm 10*4.6 mm, Dr. Maisch

Column 2: Stability 120 BS-C23 3 μm 150*4.6 mm, Dr. Maisch

% H2O + 0.1% % ACN + 0.1% Min TFA TFA Valve 1 Valve 2 0 72 28 Inject Load 3 72 28 Inject Inject 20 60 40 25 5 95 35 5 95

Products:

Lu-177: lot Lu-12-052-01/121042, Activity 2 GBq/200 μl 0.04M HCL, itg (ITM AG)

PP-F11N: 0.25 mM H₂O solution

Ammonium solution: Sigma-Aldrich metal free

Na Ascorbate: Sigma-Aldrich

HCl 30%: sigma-Aldrich nmetal free

H2O: from Milipore system Biotel

Labelling of the peptide PPF11N with Lu-177:

The Labelling of Lu-177 with the PPF-11N was made with an isotope:peptide ratio of 1:47.

Mixture of Lu-177 with peptide to an eppendorf 1.5 ml 1 w binding:

-   -   20 μl Lu-177 (190 MBq)     -   5 μl Ammonium ascorbate 0.7M     -   50 μl PPF-11N 0.25 mM     -   5 μl HCl 0.04M

The mixture was heated for 20 minutes at 95° C.

Afterwards the complex was purified and checked with HPLC methods.

Two syntheses were achieved in parallel

-   -   Purification of labelling peptide with HPLC

The two labellings reaction was injected into a 2 D HPLC.

-   -   Description of 2D HPLC:         -   First step: inject the product into the loop with a rheodyne             manual injector and push the product with a first pump             through the column 1. The product is transferred from loap             to the column 1 and is washed with H2O+0.1TFA.         -   Second Step: start the gradient with a second pump and             change the position of the valve to connect in serial the             column 1 and column 2.         -   The product is push from column 1 in column 2. The excess of             peptide is separed of the labeled Lu-177-PPF11N in the             column 2 and is collected with a fraction size of 500 ul.             The collected tube contains still 5 mg Na-ascorbate.     -   Result of purification with HPLC

Activity Collection [MBq] % time [min] Volume [μl] Injected 378 100 80 activity Remainder 30 8 eppendorf tube Fraction 3 120 31 12.5-13.0 500 Fraction 4 180 48 13.0-13.5 500

Preparation of the labeled peptid for mouse i.v. injection

The two fractions have been fused and the solvent was evaporated during 35 min.

Afterwards 600 ul PBS 1× with 10 ul 5 mM DTPA solution was added.

Final solution: 295 MBq/610 ul.

Stability

12 MBq of the radiolabelled compound was incubated in 2 mL fresh human plasma. A 40 μL probe was taken after 0, 1, 2, 18, 24, 48 and 72 h and added 200 μL (50% Methanol and 50% Acetonitril) in a Mini-UniPrep Filter. The solution is filtered after vortexing. 40 μL of the filtered solution is analyzed by HPLC.

Biodistribution Studies

CD1 nu/nu mice were injected with 5×10⁶ A431 cells. CCK-2 receptor positive A431 cells' were injected into one flank and mock cells on the other as an unspecific control. The tumors reach a weight of about 80 to 120 mg after about 10 days. 150-200 kBq (5 pmol) of the radiolabelled peptides were injected into the tail vein. Mice were killed by CO₂ asphyxiation after defined time points post injection. The organs were dissected, weighted and the activity was measured. The % injected activity per gram (% i.A./g) was calculated. The animal experiments were approved by the local animal welfare committee and performed according to national regulations.

DISCUSSION

-   1. Aloj L, Caraco C, Panico M, Zannetti A, Del Vecchio S, Tesauro D,     De Luca S, Arra C, Pedone C, Morelli G, Salvatore M. In vitro and in     vivo evaluation of 111In-DTPAGlu-G-CCK8 for cholecystokinin-B     receptor imaging. J Nucl Med. 2004; 45(3):485-494. -   2. Lehenberger S, Barkhausen C, Cohrs S, Fischer E, Grunberg J, Hohn     A, Koster U, Schibli R, Turler A, Zhernosekov K. The low-energy     beta(−) and electron emitter (161)Tb as an alternative to (177)Lu     for targeted radionuclide therapy. Nucl Med Biol. 38(6):917-924. 

1-9. (canceled)
 10. A mini-gastrin analogue PP-F11, comprising: a formula: PP-F11-X-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Y-Asp-Phe-NH₂, wherein Y stands for an amino acid replacing methionin and X stands for a chemical group attached to a peptide for at least one of a diagnostic intervention or a therapeutic intervention at CCK-2 receptor relevant diseases.
 11. The mini gastrin analogue PP-F11 according to claim 10, wherein the methionin is replaced by a norleucin.
 12. The mini gastrin analogue PP-F11 according to claim 10, wherein the X stands for a radio nuclide.
 13. The mini gastrin analogue PP-F11 according to claim 10, wherein the X stands for an optically active chemical compound.
 14. The mini gastrin analogue PP-F11 according to claim 10, wherein the X stands for a chemotherapeutic active compound.
 15. The mini gastrin analogue PP-F11 according to claim 10, wherein the X stands for a nanoparticle or a liposome which have a diagnostic function or which have a therapeutic function by themselves or are loaded with an active compound.
 16. The mini gastrin analogue PP-F11 according to claim 12, wherein said radio nuclide is selected from the group consisting of ¹⁷⁷Lu, ⁹⁰Y and ¹¹¹In.
 17. The mini gastrin analogue PP-F11 according to claim 15, wherein said nanoparticle or said liposome are an optical active or MRI contrast agent.
 18. A method of performing an intervention, which comprises the step of: providing a mini-gastrin analogue PP-F11 having a formula: PP-F11-X-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Y-Asp-Phe-NH2, wherein Y stands for an amino acid replacing methionin and X stands for a chemical group attached to a peptide for a diagnostic intervention at CCK-2 receptor relevant diseases.
 19. A method of performing an intervention, which comprises the step of: providing a mini-gastrin analogue PP-F11 having a formula: PP-F11-X-DGlu-DGlu-DGlu-DGlu-DGlu-DGlu-Ala-Tyr-Gly-Trp-Y-Asp-Phe-NH₂, wherein Y stands for an amino acid replacing methionin and X stands for a chemical group attached to a peptide for a therapeutic intervention at CCK-2 receptor relevant diseases.
 20. The method according to claim 19, which further comprises the step of replacing the methionine by a methionine isosteric amino acid with no oxidation potential and showing a high tumor affinity. 